Question

我运行此代码作为imageView的扩展，将图像加载到单元格。问题是图像正在加载到单元格，但所有单元格图像都是不可见或隐藏的，直到我点击其中一个图像后显示所有单元格图像！

extension UIImageView {
func downloadImageFrom(link:String, contentMode: UIViewContentMode) {
    URLSession.shared.dataTask( with: NSURL(string:link)! as URL,    completionHandler: {
        (data, response, error) -> Void in
        DispatchQueue.main.async {
            self.contentMode =  contentMode
            if let data = data { self.image = UIImage(data: data) }
        }
    }).resume()
}
}

并在cellforRowAt：

    cell.imageView?.downloadImageFrom (link)

Answer 1

在问题上发布的信息较少我仍然可以假设以下可能是问题

- ＆GT;您的单元格有UIImageView并且您正在下载图像但是在图像下载后如何通知单元格？，

- ＆GT;由于tableview重用单元格和你的imageview也将被你的代码中的tableview单元重用，你只需要下载图像数据并设置为UIImageView，这将在未来产生问题

提示：

1）使用磁盘或内存缓存，

2）在单元格下载图像时使用占位符图像

3）使用完成处理程序（闭包）在完成下载后通知您的单元格

4）您可以使用非常容易使用的第三方库，如AlamofireImage或SDWebImage

Answer 2

您可以使用以下代码： -

 extension UIImageView {

 static let cacheData = NSCache<AnyObject, AnyObject>()
 func downloadedFrom(link: String, placeHolder:String = "placeholder",isFromCache:Bool = true,isIndicator:Bool = true,isAppendBaseUrl:Bool = true) {

    let placeHolderImage = UIImage.init(named: placeHolder);
    self.contentMode = UIViewContentMode.scaleAspectFill
    self.clipsToBounds = true;
    self.image=placeHolderImage;
    var strlink = ""

    if isAppendBaseUrl
    {
        strlink =  "Your base url" +  link
    }
    else
    {
        strlink = link
    }
    let activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: UIActivityIndicatorViewStyle.whiteLarge)
            guard let url = URL(string: strlink) else
            {
                return
            }
            if isIndicator
            {
                activityIndicator.center = CGPoint(x: self.bounds.size.width/2, y: self.bounds.size.height/2)
                activityIndicator.color = UIColor.white
                self.addSubview(activityIndicator)
                activityIndicator.startAnimating()
            }
            if isFromCache
            {
                if let cachedImage = UIImageView.cacheData.object(forKey: url as AnyObject) as? UIImage
                {

                    if isIndicator
                    {
                        activityIndicator.stopAnimating()
                    }
                    self.image = cachedImage
                }
                else
                {
                    self.image = placeHolderImage
                    let urlStr = strlink
                    let url = URL(string: urlStr)

                    let request: URLRequest = URLRequest(url: url!)


                    URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in

                    if error != nil
                    {
                        print(error!)

                        return
                    }
                        DispatchQueue.main.async(execute: { () -> Void in
                            let image = UIImage(data: data!)
                            if isIndicator
                            {
                                activityIndicator.stopAnimating()
                                activityIndicator.removeFromSuperview();
                            }
                            if (image != nil)
                            {
                            self.image = image

                            UIImageView.cacheData.setObject(image!, forKey: url as AnyObject)
                            }

                        })


                }).resume()
                }
            }
            else
            {
            self.image=placeHolderImage;
                let urlStr = strlink
                let url = URL(string: urlStr)

                var request: URLRequest = URLRequest(url: url!)

                request.setValue("xyz", forHTTPHeaderField:"DeviceId")

                URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in

                    if error != nil
                    {
                        print(error!)

                        return
                    }
                    DispatchQueue.main.async(execute: { () -> Void in
                        let image = UIImage(data: data!)
                        if isIndicator
                        {
                            activityIndicator.stopAnimating()
                            activityIndicator.removeFromSuperview();
                        }
                        if (image != nil)
                        {
                            self.image = image

                            UIImageView.cacheData.setObject(image!, forKey: url as AnyObject)
                        }

                    })
                }).resume()}
}}

Answer 3

我通过在表格单元格中添加子视图并保存图像来解决我的问题

Answer 4

试试这个，它对我有用。可能忘了指定方法super.viewDidLoad（）或super.viewDidAppear（true）......

PDPageContentStream contentStream = PDPageContentStream(originalDoc, page1, PDPageContentStream.AppendMode, true, true);

在tableview asynch中加载图像

4 个答案: